The present invention relates to a magnetic tape cassette characterized by a window frame structure of a magnetic tape cassette having a window member for confirming the winding amount of the magnetic tape, a window member, and a resin product.
Generally, in audio devices and video devices, a magnetic tape cassette is used very much, in which recording and playing operations are performed while a magnetic tape wound onto a pair of tape reels is being held within the cassette case so that it can run.
As shown in FIG. 6, for example, a magnetic tape cassette 50 used for DVC (digital video cassette) has a cassette case which is constituted by upper and lower halves 51, 52. Their upper and lower halves 51, 52 are fitted to each other and tightened by a plurality of screws. And, a pair of tape reels 53, 53 formed by welding an upper flange and a hub with which a lower flange is integrally formed are rotatably stored in the cassette case in a state where a magnetic tape 52 is wound onto the tape reels.
Tape guides 55, 55 are provided on both sides of an opening portion 56 on a front-end side in the lower half 52. Each tape guide 55 guides the magnetic tape 57 that is fed out from one tape reel 53 and wound onto the other tape reel 53, and causes the magnetic tape 57 to pass through the predetermined position in the opening portion 56.
Further, on a rear end side of the lower half 52, a tape reel lock member 58 having a tape reel fixing arm 58a is incorporated. The tape reel lock member 58 is energized by a compressive coil spring 59, whereby the tape reel fixing arm 58a is fitted to fitting teeth 53a formed on the periphery of the lower flange of each tape reel 53 thereby to prevent unexpected rotation of each tape reel 53. Hereby, looseness of winding of the magnetic tape 57 is prevented.
Further, a reel energizing plate spring 63 is attached to a top plate 51a of the upper half 51 in relation to each tape reel 53. Each reel energizing plate spring 63 is overhung by the upper half 51 and energizes the corresponding tape reel 53 on the lower half 52 side.
Further, an outer lid 60, a top lid 61 and an inner lid 62 which cover a front surface and a rear surface of the magnetic tape 57 laid between a pair of the tape guides 55 in the lower half 52 are openably and closeably attached on the front end side of the upper half 51 in order to obtain dustproof ability with which the tape cassette is fit for outdoor use.
On one side (on right side in the figure) in the longitudinal direction of the top plate 51a of the upper half 51 in this magnetic tape cassette 50, a window opening 65 which extends in the short direction of the top plate 51a is formed so that the winding amount of the magnetic tape 57 (residual amount) onto the tape reel 53 can be confirmed. And, a transparent window member 64 is attached so as to close the window opening 65.
As shown in FIG. 7, the window member 64 formed substantially in the shape of a hexagon has a plurality of welded ribs 66 on a fixed surface 64a formed at the periphery of the window member. On the other hand, at the periphery of the window opening 65 formed in the top plate 51a of the upper half 51, a fixing surface 65a for fixing the window member 64 thereto is formed. The thickness of the portion where its fixing surface 65a is formed is made thinner than that of the top plate 51a. The fixing surface 65a continues to the surface of the top plate 51a through a slant 67. Further, at a portion surrounding the fixing surface 65a, positioning ribs 68 are formed on each side of the window opening 65. Further, since a corner portion B that is a part of the portion surrounding the fixing surface 65a is located immediately below the overhung end portion of the reel energizing plate sprint 63, it is a flat surface that continues to the surface of the top plate 51a but not the slant.
In order to attach this window member 64 onto the upper half 51, the window opening 65 is firstly covered with the window member 64 while the window member 64 is being guided by the positioning ribs 68, and the welded ribs 66 of the window member 64 are placed onto the fixing surface 65a of the peripheral portion of the window opening 65. Then, in a state where the window member 64 is pressed against the fixing surface 65a of the peripheral portion of the window opening 65, the welded ribs 66 of the window member 64 are welded onto the fixing surface 65a by ultrasonic vibration or the like, as shown in FIG. 8.
On the other hand, the fixing surface 65a onto which the window member 64 of the upper half 51 is welded has a difference-in-level in relation to the surface (inner surface or outer surface) of the top plate 51a. In case that the thickness changes suddenly at the portion of this difference-in-level, crape transfer defect is produced due to a reason why time for which the pressure is applied is different at the injection molding time or other reasons, so that there is fear that the appearance of the surface of the upper half 51 will be damaged. Such crape transfer defect means that a crape surface is not formed on a portion of the external surface on the cassette or the product.
Therefore, in the upper half 51, as described above, the fixing surface 65a continues to the surface of the top plate 51a through the slant 67, whereby the sudden change of the pressure at the injection molding time is avoided and the bad appearance of the upper half is prevented.
However, in the cassette case adopting the window frame structure like this, when an external force is applied onto the window member 64, it acts concentratedly on a corner portion C on the opening portion side through which the magnetic tape in the cassette case passes, whereby the window member 64 frequently peels off from the fixing surface 65a of the periphery of the window opening 65, and particularly from the vicinity of the corner portion C onto which the concentrated load acts. This is a problem.
On the other hand, in the above conventional magnetic tape cassette 50, the window member 64 is formed by resin injection molding. At this time, as shown in FIG. 9, a fine line like a hair line that is formed at a portion where more than two streams of the molten resin join, that is, a weld line W is produced in the window member 64.
The conventional window member 64 has adopted such a constitution that a gate position is set to a position shown by reference numeral 69, and that a valve gate is divided into three before a portion leading to a gate outlet and their divided valve gates are joined before the gate outlet. Accordingly, the weld line produced in the junction before the gate outlet flows intactly together with the melted resin, and as shown in FIG. 6, the weld line W is frequently produced between the welded ribs 66, 66 that are comparatively near the gate position 69.
In case that the window member 64 in this state is going to be welded onto the fixing surface 65a formed on the periphery of the window opening 65 of the upper half 51 by the ultrasonic vibration, there is an occasion that a crack starts from the weld line W. This is a problem.
It is an object of the present invention to solve the aforementioned problem.
A first object of the invention is to reliably weld the window member to the upper half.
A second object of the invention is to provide a magnetic tape cassette that prevents the window member from peeling off without damaging the appearance and with the simple structure.
A third object of the invention is to provide a resin product having no fear of the crack even in case that the resin product is firmly attached to some product by welding.
The object of the invention can be achieved by a magnetic tape cassette comprising a cassette case having upper and lower halves, a tape reel which winds thereto a magnetic tape that passes through an opening portion of the cassette case and which is stored into the cassette case, and a window member set to a window opening formed in a top plate of the upper half; in which a fixing surface for fixing the window member is formed onto a peripheral portion of the window opening formed on the top plate of the upper half, and a slant that continues to the fixing surface is formed at a portion surrounding the fixing surface. In this magnetic tape cassette, a build-up portion is formed at the portion surrounding the fixing surface and at a corner portion on the opening portion side of the cassette case through which the magnetic tape passes.
Further, the object of the invention can be achieved by a magnetic tape cassette comprising a cassette case having upper and lower halves, a tape reel which winds thereto a magnetic tape that passes through an opening portion of the cassette case and which is stored into the cassette case, and a window member set to a window opening formed in a top plate of the upper half; in which a fixing surface for fixing the window member is formed onto a peripheral portion of the window opening that is formed on one side in the longitudinal direction of the top plate of the upper half and extends in the short direction of the top plate, and a slant that continues to the fixing surface is formed at a portion surrounding the fixing surface. In this magnetic tape cassette, a build-up portion is formed at the portion surrounding the fixing surface, and at a corner portion on the opening portion side of the cassette case through which the magnetic tape passes and on the center side in the longitudinal direction of the top plate.
Here, as the build-up portion, it is preferable to use a reinforcement rib having the same thickness as the top plate of the upper half. In addition, as the build-up portion, it is also preferable to use a chamfering portion which is defined by connecting both ends of a circular arc of the corner portion in a straight line.
According to the magnetic tape cassette of the invention, occurrence of the crape transfer defect is prevented by forming the slant at the portion surrounding the fixing surface, and strength is obtained and a shape hard to deform is provided by forming the build-up portion at the corner portion on the opening portion side of the cassette case.
The above object of the invention can also be achieved by a magnetic tape cassette in which a welded rib of a window member, which is formed at the peripheral portion of the window member, is brought into contact with a fixing surface formed at a peripheral portion of a window opening of an upper half, and the window member is welded onto the fixing surface of the upper half by ultrasonic vibration. This magnetic tape cassette is characterized in that a weld line produced by the resin molding of the window member is positioned on the welded rib.
Further, the above object of the invention can be achieved by a window member forming a plurality of welded ribs at the peripheral portion thereof, wherein a weld line produced by the resin molding is positioned on the welded rib.
Further, the above object of the invention can be achieved by a resin product forming a plurality of welded ribs, wherein a weld line produced by the resin molding is positioned on the welded rib.
According to the invention, by setting the gate position to the suitable position, the weld line is formed on the welded rib to be welded to some member. Namely, the gate position is set suitably in such a manner that the weld line is formed not between the welded ribs but on the welded rib that is thicker than other portions of the resin product.
Accordingly, even when the resin product is going to be welded to some product by the ultrasonic vibration, since the weld line is set on the welded rib, the crack does not start from the weld line W.